Sunday, February 28, 2016

A couple of quick notes on Mercury #1

I'm trying to learn about Mercury programming language. Here's a quick list of things I learned recently about it.

Getting a Windows version of the Mercury compiler

I was able to get a version of the Mercury compiler by downloading a "Release of the day" version from here:

I just followed the instructions from INSTALL file. The only requirement is to have a Cygwin version installed.

Operations are associated with a data type

For example the predicate for performing an operation N times is defined in the int module (int.fold_up, int_fold_down).

Predicates can be partially applied

Mercury supports a mechanism similar to currying in other languages.

For example, in the following invocation to int.fold_up we're not specifying values or variables for the last three arguments(these are resolved by the application inside int.fold_up):

:- pred write_pixel_data(
        int::in,  % width
        int::in,  % height
        int::in,  % padding
        int::in,  % idx
        io::di, io::uo) is det.
            Width * 3,
            (RowWidth - (Width * 3))),0,(RowWidth*Height) - 1,!IO)

Bitwise operators look nice!

For example bitwise "and" look like:

   io.write_byte(Stream, (IntValue >> 8) /\ 0xFF,!IO), 

Code for this post can be found here

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